Omnidirectional pressurized hydraulic and pneumatic fluid-actuated piston-type power means for operating mechanisms, such as a chuck, by reciprocating linear movements, omnidirectionally, within any plane

ABSTRACT

A hydraulically or pneumatically controlled apparatus for operating a chucking tool on a lathe or other machine tool for clamping and releasing workpieces. Due to its particular structure and especially the particular design and arrangement of its check valves, this apparatus takes up a very small space, and the axial movements of its piston are transmitted to the outside and may be employed for controlling the operations of the machine tool.

Elite Sates atet Kodalle [54] OMNIDIRECTIONAL PRESSIJRIZED HYDRAULIC ANDPNEUMATIC FLUID- ACTUATED PISTON-TYPE POWER MEANS FOR OPERATINGMECHANISMS, SUCH AS A CHUCK, BY RECIPROCATING LINEAR MOVEMENTS,OMNIDIRECTIONALLY, WITHIN ANY PLANE [72] Inventor: Rudi Kodalle,Sontheim 95m c Rohm-Gesdlschafi m.b.H. Werkzeugund Maschinenfabrik,Sontheim am Brenz, Germany 22 Filed: Jan. 23, 197 0 I [21] Appl. No.:5,305

[30] Foreign Application Priority Data Mar. 7, 1969 Germany ..P 19 11558.3

am Brenz.

[73] Assignee:

[52] U.S.Ci ..91/I,91/420,91/422,

92/106 [51] lnt.Cl ..F0lb31/12,F15b 13/042 [58] Field oi Search..91/422, 1, 420; 92/106; 279/4 PRESSUf/ZED FLU/0 7'0 FIOW 0F FLU/DIND/CA Feb. 15,1972

[56] References Cited UNITED STATES PATENTS 2,964,016 12/1960 3,126,7063/1964 3,303,755 2/1967 3,369,464 2/1968 3,411,415 11/1968 Benjamin etal. ..9l/422 X FOREIGN PATENTS OR APPLICATIONS 893,678 4/1962 GreatBritain ..91/420 Dettinger Linker et Primary Examiner-Edgar W. GeogheganAssistant Examiner-Irwin C. Cohen An0meyOtto John Munz [5 7] ABSTRACT Ahydraulically or pneumatically controlled apparatus for operating achucking tool on a lathe or other machine tool for clamping andreleasing workpieces. Due to its particular structure and especially theparticular design and arrangement of its check valves, this apparatustakes up a very small space, and the axial movements of its piston aretransmitted to the outside and may be employed for controlling theoperations of the machine tool.

9 Claims, 2 Drawing Figures PATENTEU EB 1 I972 FLU/D FIG] lA/VE/VTORRUDI KODALLE OMNIDIRECTIONAL PRESSURIZED HYDRAULIC AND PNEUMATICFLUID-ACTUATED PISTON-TYPE PDWER MEANS FOR OPERATING MECHANISMS, SUCH ASA CHUCK, BY RECIPROCATING LINEAR MOVEMENTS, OMNIDIRECTIONALLY, WITHINANY PLANE The present invention relates to a rotary chucking cylinderfor tightening and releasing a chucking tool of a lathe or other machinetool by means of a pneumatic or hydraulic pressure medium which actsupon a piston which is axially slidable within the cylinder and mountedon a shaft which is connected to and rotatable within a distributorhousing. This shaft is provided with two channels each of which has oneend communicating with a connection fitting on the distributor housingfor the supply and discharge of the pressure medium, while its other endleads to the cylinder chamber at one or the other side of the piston.The flow of the pressure medium through the two channels is controlledby a pair of check valves in such a manner that the supply of pressuremedium through one channel opens both check valves and fiows into onecylinder chamber and thereby shifts the piston, while the pressuremedium which is thereby expelled from the other cylinder chamber flowsoff through the other channel.

If for any reason the supply of the pressure medium to such a chuckingcylinder might drop or be interrupted entirely, both check valves andthus also both cylinder chambers will immediately be closed so that thepiston will be locked in a fixed position. Consequently, the chuckingtool which is operated by the chucking cylinder will likewise remain inits last position even when the pressure supply drops or ceases entirelyso that, if this was its tightened or clamping position, the workpiecewill remain tightly clamped therein and cannot fallout.

it is an object of the present invention to provide a chucking cylinderof the type as described above which has the advantage that it is of amuch smaller and more compact size than similar apparatus as previouslyemployed by mounting the check valves on the piston of the cylinder andin a manner so as to take up very little space, and that due to thisconstruction the operation of this apparatus is very reliable and it maybe manufactured and assembled at a low cost.

A further object of the invention is to design this chucking cylinder sothat the movements of its piston are transmitted to the outside wherethey may be employed for indicating the operating positions of thepiston and/or for supervising or con trolling the operations of themachine tool, for example, by insuring that certain operations of themachine tool will not be carried out until by the position of its pistonthe chucking cylinder has indicated that the workpiece is properlyclamped by or released from the chucking tool.

According to the invention, these objects are attained by mounting thecheck valves on the piston within the cylinder so as to be bodilymovable with the piston but to operate in a direction transverse to theaxial movements of the piston, by mounting the shaft of the piston inwhich the channels for supplying and discharging the pressure medium areprovided so as to be rotatable with the cylinder but slidable in itsaxial direction in the front and rear walls of the cylinder, and bymounting the distributor housing on this shaft outside of the cylinderso as to be nonrotatable but to be taken along by this shaft when it ismoved in its axial direction by the piston.

Since the axial movements of the shaft carrying the piston andcontaining the channels leading to the check valves in or on the pistonare directly transmitted to the distributor housing, the inventionfurther provides that the distributor housing carries or is operativelyassociated with suitable means for indicating the different operatingpositions of the piston and/or for employing the movements of the pistonfor supervising or controlling the operations of the machine tool.

According to the invention, the two check valves are mounted on thepiston and each of them comprises a valve cage containing a valvechamber which has an aperture in its bottom forming a valve seat whichcommunicates with one of the channels and is normally closed by a valveplate and may LII be opened toward the inside of the valve chamberagainst the action of a spring by the pressure of the pressure mediumwhich is supplied through the mentioned channel and which then flowsfrom the valve chamber through a valve part toward one or the othercylinder chamber.

The two valves may be of an especially simple design if they arecombined into a single structural unit which is mounted on the piston soas to extend transverse to its axis so that the two valve chambers aredisposed diametrically opposite to each other at both sides of thepiston axis and are separated from each other by an intermediate centralcylindrical chamber in which a small control piston is slidable which isprovided with tappets on its opposite ends. When the pressure medium issupplied through one channel and the associated check valve into onecylinder chamber at one side of the main piston, it also acts at thesame time upon the control piston and moves the same in the directiontoward the other check valve so that one of the tappets then pressesagainst the valve disk of this other valve and opens the same againstthe action of its spring. Thus, while the pressure medium flows throughthe first channel and the first check valve into one cylinder chamberand thereby shifts the piston in one direction, the pressure mediumwhich is expelled by the piston from the other cylinder chamber can passthrough the second check valve which has been opened by the tappet onthe small control piston and through the second channel in the shaft tothe distributor from which it may be discharged through one of theconnection fittings thereon. If this first operation of the chuckingcylinder was carried out, for example, for clamping a workpiece in thechucking tool and is subsequently to be followed by a second operationof the chucking cylinder in which the main piston is moved in theopposite direction, for example, for releasing the workpiece from thechucking tool, the pressure medium is passed through the second channelin the shaft and flows through the second check valve into the cylinderchamber at the rear of the piston, while at the same time this pressuremedium also acts upon the small control piston which by its tappet thenopens the first check valve so that, while the main piston movesforwardly, the pressure medium which is expelled from the cylinderchamber in front of this piston passes through the first check valve andthe associated channel toward and from the distributor.

Another feature of the invention consists in mounting the mentionedcheck valve unit in a very simple manner on the main piston by providingthe latter with a bore which extends transverse to the piston axis andinto which the mentioned valve unit is to be inserted, by extending thetwo channels of the piston shaft for the pressure medium so that theirfront ends terminate into this bore, by providing in each side of thepiston a short axial bore which terminates into the transverse bore intowhich the valve unit is inserted and then connects the valve part of oneof the other check valves with one cylinder chamber or the other Thedistributor housing which is mounted on and movable in the axialdirection together with the piston shaft but is nonrotatable is providedwith two connection fittings each of which communicates at the inside ofthe housing with one of the channels of the shaft through either ofwhich the pressure medium may at one time be supplied to one of thechannels or the other, while the return flow of the expelled pressuremedium passes through the other channel and the other connection fittingon the distributor housing.

On its outside, this distributor housing may be provided with means forindicating the operating positions of the chucking cylinder and thusalso of the chucking tool and/or with means for employing the axialmovements of the distributor housing for supervising or controlling theoperations of the machine tool. These means which may consist, forexample, of suitable cams, electric switch means or switch'actuatingmeans, or the like are preferably mounted on the distributor housing soas to be easily exchangeable. For this purpose, the connection fittingson this housing for supplying and discharging the pressure medium mayalso be designed so as to permit these indicating or control means to beremovably mounted thereon.

The features and advantages of the present invention will become furtherapparent from the following detailed description thereof which is to beread with reference to the accompanying drawings, in which:

FIG. 1 shows a central longitudinal section of a chucking cylinderaccording to the invention, in which for a better illustration theconnection fittings on the distributor housing are turned at an angle of90 to their preferred position as shown in FIG. 2; while FIG. 2 shows across section which is taken along the line lI-II ofFlG. 1.

Referring to the drawings, the chucking cylinder according to thepresent invention which serves for tightening and releasing a chuckingtool (not shown) of a lathe or other machine tool comprises a cylinder 1which forms an outwardly sealed housing, a piston 2 which is axiallyslidable within cylinder 1 but rotatable together with the cylinder, anda shaft 7 which is secured to or integral with piston 2 and projectsfrom both sides of the piston and extends slidabiy through the rear walland the cover of cylinder 1 to the outside. The forwardly projecting endof shaft 7 is provided with a tapped bore into which the threaded end ofa tie rod (not shown) of the chucking tool may be screwed which usuallyextends through the hollow spindle of the machine tool to the rear endof which the cover of cylinder 1 is to be secured so that cylinder 1together with piston 2 and shaft 7 will be rotated by the spindie.

By means of shaft 7, cylinder 1 is connected to a distributor which isgenerally designated by the numeral 4 and comprises a distributorhousing 5 which is mounted so as not to be rotatable with shaft 7 butconnected to the latter so as to follow its movements in axialdirections. For this purpose shaft 7 is rotatably mounted within housing5 on bearings 8 and 9 and bearing 9 abuts at one side against a shoulder10 on the inner wall of housing 5, while its other side abuts against aspring ring 11 on the rear end of shaft 7 so that housing 5 issubstantially immovable in its axial direction relative to shaft 7. Thisshaft which carries the piston 2 is axially slidable through bores inthe cover and rear wall of cylinder 1 and is sealed relative to theoutside by suitable gaskets 16 in this cover and rear wall. Any axialmovement of piston 2 in the direction of the double arrow 17 as shown inFIG. 1 will therefore be positively transmitted by shaft 7 to thedistributor housing 5.

On its inner side, housing 5 is provided with a pair of annular grooves12 and 13 which directly communicate with connection fittings 6 througheither of which the pressure medium, for example, compressed air or oil,is supplied or discharged. If the chucking cylinder is operatedhydraulically, any oil which might leak through the joints between shaft7 and housing 5 will be collected in a channel 14 in the wall of thehousing from which it is discharged through an outlet connection 1S.

Shaft 7 is provided with two channels 18 and 19 which extendlongitudinally through this shaft from its rear end and terminate into atransverse bore in piston 2 into which a pair of check valves are to beinserted and which communicates through a bore 24 with the cylinderchamber 40 in front of the piston 2 and through another bore 25 withcylinder chamber 39 at the rear of the piston. The part of shaft 7 whichextends into the distributor housing 5 is provided with a bore in thewall of each channel 18 and 19 which directly communicates with theannular groove 12 or 13 with which one or the other connection fitting 6is connected in the inner wall of housing 5.

For controlling the flow of the pressure medium into or from the twopressure chambers 39 and 40 in cylinder 1 at the opposite sides ofpiston 2, a pair of check valves, generally designated by the numerals20 and 21, are mounted on piston 2. According to a preferred embodimentof the invention as il lustrated in the drawings, piston 2 is for thispurpose provided with a bore which extends transverse to the axis ofshaft 7. Channels 18 and 19 terminate at their front ends into this borewhich communicates with chambers 39 and 40 through the axial bores and24, respectively, which extend in opposite directions through the wallof the transverse bore into these chambers. Since, as subsequentlydescribed in detail, a small control piston 35 is inserted into thetransverse bore in a position between the front ends of the two channels18 and 19, channel 18 is adapted to communicate through check valve 20and bore 24 only with the cylinder chamber 40 in front of piston 2,while channel 19 can communicate through check valve 21 and bore 25 onlywith the cylinder chamber 39 at the rear of piston 2 when the respectivecheck valve is opened.

Each check valve 20 and 21 consists of a valve cage 26 or 27 whichencloses a valve chamber 22 or 23, respectively. The bottom of each ofthese cages is provided with a bore forming an inner valve seat 28 or 29which is normally closed by a valve plate 32 or 33 under the action of aspring 30 or 31 and is adapted to be opened toward the inside of therespective valve chamber if a pressure medium, for example, compressedair or oil, is supplied through channel 18 or 19 under a sufficientpressure to overcome the strength of spring 30 or 31. By being mountedin the transverse bore, the two check valves 20 and 21 are disposeddiametrically opposite to each other relative to the axis of piston 2and thus take up a very small space. As already mentioned, a smallcontrol piston 35 is located in the transverse bore between the frontends of channels 18 and 19 and it is slidable within a cylinder chamber34 in the direction toward one or the other check valve 20 or 21. Eachend of this small piston is provided with a projecting tappet 36 whichis adapted to hit against the adjacent valve plate 32 or 33 and to liftthe same off its seat 28 or 29 against the action of spring 30 or 31when a pressure medium of a sufficient pressure is supplied through thechannel 18 or 19 which terminates into the transverse bore adjacent tothe opposite end of piston 35.

According to a preferred embodiment of the invention as illustrated inFIG. 1, the two check valves 20 and 21 and the small piston 35 may becombined into a structural unit which may be inserted into one end ofthe transverse bore and be locked in the proper position therein by apair of spring rings or similar means at the opposite ends of this unit.The common tubular wall which combines the two valve cages 26 and 27also forms the cylinder for chamber 34 for the small control piston 35.Of course, this wall is provided with valve ports which are respectivelyin axial alignment with the bores 24 and 25 and with the front ends ofthe channels 18 and 19. It is evident that by combining the check valves20 and 21 and the control piston 35 into a single structural unit priorto the assembly of the entire apparatus, it is much easier to mountthese elements accurately in their proper positions than it would be ifthey had to be mounted individually on or in the piston 2.

For employing the distributor housing 5 for indicating the operativepositions and axial movements of piston 2 or for transmitting thesemovements to suitable control means, for example, for controlling theoperations of the machine tool to which the chucking cylinder accordingto the invention is connected or even for controlling the operations ofthe chucking cylinder and its piston in timed relation with themachining operations of the machine tool, the connection fittings 6 andtheir screw connections 38 on the distributor housing 5 may be employed,for example, for removably securing suitable cam means 37 thereto so asto permit them to be easily exchanged for others.

The mode of operation of the apparatus as previously described is asfollows:

If the pressure medium such as oil or compressed air, is supplied, forexample, through the connection fitting 6 leading to the annular groove13, it passes through the channel 18 in shaft 7 and, if it has asufficient pressure, it opens the check valve 21 so that it will thenpass through the valve chamber 23 and valve part 5 into the cylinderchamber 39 behind the piston 2 and thereby move the latter forwardly. Atthe same time, the pressure medium also acts upon the control piston 35so as to shift the same in the chamber 34 toward the check valve 2!whereby the tappet 36 hits against the valve plate 32 and lifts it offits seat 28 so that the pressure medium which is expelled from thecylinder chamber 40 by the forward movement of piston 2 can flow offthrough valve port 24, valve chamber 22, channel 18, the annular groove12 and the as sociated connection fitting 6 until piston 2 arrives inits final forward position as shown in FIG. 1.

If piston 2 is to be retracted from this position, for example, fortightening the chucking tool (not shown) so as to clamp a new workpiece,the operation of the chucking cylinder has to be reversed by reversingthe circuit of the pressure medium which then has to be supplied throughchannel 18 so as to open the check valve 20 and to flow through valvechamber 22 and valve port 24 into the cylinder chamber 40 in front ofpiston 2. At the same time, the pressure medium also shifts the controlpiston in the direction toward check valve 21 so that its tappet 36opens this valve and thus permits the pressure medium to be expelledfrom cylinder chamber 39 through valve port 25, valve chamber 23,channel 19, the annular groove 13 and the associated connection fitting6 to the same extent as it is supplied into chamber 40,

It is evident from the preceding description that, if any failure occursin the supply of pressure medium to one or the other channel 18 or 19 orif the pressure of this medium drops below a certain value, both checkvalves will be immediately closed by the valve springs 30 and 31 and theback pressure in chambers 39 and 40 acting upon valve plates 32 and 33,and piston 2 will remain in a locked position in cylinder 1.Consequently, the chucking tool will likewise remain in its previouscondition and a workpiece which is clamped therein will not be released.

Since due to the means 9 to 11 the distributor housing 5 must follow anyaxial movements of shaft 7 and piston 2, each movement may betransmitted by the cam or other means 37 on housing 5 to effect suitablecontrol functions.

Although my invention has been illustrated and described with referenceto the preferred embodiment thereof, I wish to have it understood thatit is in no way limited to the details of such embodiment but is capableof numerous modifications within the scope ofthe appended claims.

Having thus fully disclosed my invention, what I claim is:

1. An omnidirectional pressurized hydraulic and pneumatic fluid-actuatedpiston-type power means for operating mechanisms, such as chuck, byreciprocating linear movements, omnidirectionally, within a plane,comprising:

a revolving chucking cylinder and piston unit having a front and rearpiston chamber and a piston shaft;

a nonrotating reciprocating pressurized fluid supply and discharge meansmounted on said shaft;

a single secondary control valve unit within said piston to control theflow of said pressurized fluid alternately in the said front and rearpiston chambers and simultaneously the discharge of the pressurizedfluid from the opposite cylinder chamber, said chucking cylinder andpiston unit comprising:

an outwardly closed cylinder having front and rear walls,

each of said walls having a central bore;

a piston axially slidable in and rotatable with said cylinder anddividing the inside of said cylinder into said front chamber and saidrear chamber;

said shaft coaxially connected with said piston and having a frontsection and a rear section secured to the opposite sides of said pistonand axially slidable in said central bores of said front and rear walls;

sealing means between said walls and said shaft for sealing saidchambers;

said rear section of said shaft having a pair of longitudinal channels,a supply channel and a return channel therein;

said pressurized fluid means to alternately pressurize and dischargeeach of said channels, one to serve as a supply channel and the other asa return channel simultaneously;

said control valve unit comprising pair of check valves mounted in saidpiston;

resilient means for normally maintaining said valves in a closedposition;

each of said valves being associated with one of said channels and oneof said chambers;

actuating means to alternately open said valves against the action ofsaid resilient means if acted upon by said pressurized fluid meanspassing through said channels when serving as a supply channel, so thatsaid fluid means then flows through said valve onto one of said chambersand thereby acts upon said piston so as to move the same in one axialdirection;

said actuating means also responsive to the pressure of said fluid meanspassing through said supply channel for acting upon and to open theother check valve so that said pressurized fluid contained in the otherchamber flows out of it and through said other check valve and saidreturn channel;

said nonrotating supply and discharge means connected to a part of therear section of said shaft outside of said cylinder and movable in theaxial direction with said shaft for alternately supplying saidpressurized fluid to one of said channels and for alternatelydischarging the return flow of said fluid from said other channel.

2. A power means as defined in claim 1, each of said check valvescomprising a valve chamber having a first wall with a first bore thereinforming valve seat at the inner side of said valve chamber, and having asecond wall with a second bore therein;

said first bore of one valve member communicating at the outside thereofwith one of said channels, and said first bore of the other valvechamber communicating at the outside thereof with the other channel,said second bore of one valve chamber communicating with one cylinderchamber, and said second bore of the other valve chamber communicatingwith the other cylinder chamber;

a movable valve member in each of said valve chambers,

and a compression spring in each of said valve chambers acting upon saidvalve member and pressing the same upon said valve seat.

3. A power means as defined in claim 2, check valves mounted on saidpiston in such a position that said valve members are movable indirections at right angles to the axis of said piston and shaft.

4. A power means as defined in claim 3, said second walls of both ofsaid check valves forming a part of a common tubular member secured tosaid piston and having closed ends, and combing said check valves andsaid actuating means to form a structural unit;

said first walls of both of said check valves forming tran versepartitions in said tubular member and spaced from each other by acentral cylindrical part of said tubular member;

said actuating means consisting of a control piston slidable in saidcylindrical part and having a tappet on each end adapted to hit againstthe adjacent valve member to lift same off its seat, whereby when saidpressurized fluid is supplied through said supply and discharge meansand one of said channels and opens one of said check valves and flowsinto one of said cylinder chambers, it also shifts said control pistonin the opposite direction to the opening movement of said check valveand said control piston by one of its tappets thereby opens the othercheck valve permitting at least some of the pressurized fluid in theother cylinder chamber to flow out of it and to be discharged throughsaid other check valve, said other channel, and said supply anddischarge means.

5. A power means defined in claim 4, said piston having a transversebore extending transversely to the axis of said piston and shaft, saidvalve unit being inserted into and secured in a fixed position in saidbore, said piston having a pair of axial bores in its opposite sides andterminating into said transverse bore and each being in alignment withsaid second bore in the wall of one of said valve chambers, so that eachcylinder chamber is in communication through said aligned bores with theassociated valve chamber.

6. A power means as defined in claim 1, in which the rear section ofsaid shaft outside of said cylinder has a pair of transverse bores eachextending from the peripheral surface of said shaft into one of saidchannels, said nonrotatable supply and discharge means comprising ahousing surrounding said outer rear section and having a pair of annulargrooves in its inner wall, each of said annular grooves being in directcommunication with one of said transverse bores in said shaft, and apair of connection fittings on said housing for supplying anddischarging said pressure medium to and from said channels through saidtransverse bores in said shaft and said annular grooves in said housing.

1. An omnidirectional pressurized hydraulic and pneumatic fluidactuated piston-type power means for operating mechanisms, such as chuck, by reciprocating linear movements, omnidirectionally, within a plane, comprising: a revolving chucking cylinder and piston unit having a front and rear piston chamber and a piston shaft; a nonrotating reciprocating pressurized fluid supply and discharge means mounted on said shaft; a single secondary control valve unit within said piston to control the flow of said pressurized fluid alternately in the said front and rear piston chambers and simultaneously the discharge of the pressurized fluid from the opposite cylinder chamber, said chucking cylinder and piston unit comprising: an outwardly closed cylinder having front and rear walls, each of said walls having a central bore; a piston axially slidable in and rotatable with said cylinder and dividing the inside of said cylinder into said front chamber and said rear chamber; said shaft coaxially connected with said piston and having a front section and a rear section secured to the opposite sides of said piston and axially slidable in said central bores of said front and rear walls; sealing means between said walls and said shaft for sealing said chambers; said rear section of said shaft having a pair of longitudinal channels, a supply channel and a return channel therein; said pressurized fluid means to alternately pressurize and discharge each of said channels, one to serve as a supply channel and the other as a return channel simultaneously; said control valve unit comprising pair of check valves mounted in said piston; resilient means for normally maintaining said valves in a closed position; each of said valves being associated with one of said channels and one of said chambers; actuating means to alternately open said valves against the action of said resilient means if acted upon by said pressurized fluid means passing through said channels when serving as a supply channel, so that said fluid means then flows through said valve onto one of said chambers and thereby acts upon said piston so as to move the same in one axial direction; said actuating means also responsive to the pressure of said fluid means passing through said supply channel for acting upon and to open the other check valve so that said pressurized fluid contained in the other chamber flows out of it and through said other check valve and said return channel; said nonrotating supply and discharge means connected to a part of the rear section of said shaft outside of said cylinder and movable in the axial direction with said shaft for alternately supplying said pressurized fluid to one of said channels and for alternately discharging the return flow of said fluid from said other channel.
 2. A power means as defined in claim 1, each of said check valves comprising a valve chamber having a first wall with a first bore therein forming valve seat at the inner side of said valve chamber, and having a second wall with a second bore therein; said first bore of one valve member communicating at the outside thereof with one of said channels, and said first bore of the other valve chamber communicating at the outside thereof with the other channel, said second bore of one valve chamber communicating with one cylinder chamber, and said second bore of the other valve chamber communIcating with the other cylinder chamber; a movable valve member in each of said valve chambers, and a compression spring in each of said valve chambers acting upon said valve member and pressing the same upon said valve seat.
 3. A power means as defined in claim 2, check valves mounted on said piston in such a position that said valve members are movable in directions at right angles to the axis of said piston and shaft.
 4. A power means as defined in claim 3, said second walls of both of said check valves forming a part of a common tubular member secured to said piston and having closed ends, and combing said check valves and said actuating means to form a structural unit; said first walls of both of said check valves forming transverse partitions in said tubular member and spaced from each other by a central cylindrical part of said tubular member; said actuating means consisting of a control piston slidable in said cylindrical part and having a tappet on each end adapted to hit against the adjacent valve member to lift same off its seat, whereby when said pressurized fluid is supplied through said supply and discharge means and one of said channels and opens one of said check valves and flows into one of said cylinder chambers, it also shifts said control piston in the opposite direction to the opening movement of said check valve and said control piston by one of its tappets thereby opens the other check valve permitting at least some of the pressurized fluid in the other cylinder chamber to flow out of it and to be discharged through said other check valve, said other channel, and said supply and discharge means.
 5. A power means defined in claim 4, said piston having a transverse bore extending transversely to the axis of said piston and shaft, said valve unit being inserted into and secured in a fixed position in said bore, said piston having a pair of axial bores in its opposite sides and terminating into said transverse bore and each being in alignment with said second bore in the wall of one of said valve chambers, so that each cylinder chamber is in communication through said aligned bores with the associated valve chamber.
 6. A power means as defined in claim 1, in which the rear section of said shaft outside of said cylinder has a pair of transverse bores each extending from the peripheral surface of said shaft into one of said channels, said nonrotatable supply and discharge means comprising a housing surrounding said outer rear section and having a pair of annular grooves in its inner wall, each of said annular grooves being in direct communication with one of said transverse bores in said shaft, and a pair of connection fittings on said housing for supplying and discharging said pressure medium to and from said channels through said transverse bores in said shaft and said annular grooves in said housing.
 7. A power means as defined in claim 9, further comprising externally mounted mechanical indicating means relative to said fluid supply and discharge unit and actuated thereby for monitoring the axial positions of said piston relative to said cylinder.
 8. A power means as defined in claim 6, further comprising means on said housing for connecting control means thereto.
 9. A power means as defined in claim 8, in which at least one of said connection fittings also serves for connecting said control means to said housing. 